Detailed example of MySQL (5.6 and below) parsing JSON

#json parsing function DELIMITER $$
DROP FUNCTION IF EXISTS `json_extract_c`$$
CREATE FUNCTION `json_extract_c`(
details TEXT,
required_field VARCHAR (255)
) RETURNS TEXT CHARSET latin1
BEGIN
SET details = SUBSTRING_INDEX(details, "{", -1);
SET details = SUBSTRING_INDEX(details, "}", 1);
RETURN TRIM(
  BOTH '"' FROM SUBSTRING_INDEX(
    SUBSTRING_INDEX(
      SUBSTRING_INDEX(
        details,
        CONCAT(
'"',
          SUBSTRING_INDEX(required_field,'$.', -1),
'":'
        ),
-1
      ),
',"',
1
    ),
':',
-1
  )
) ;
END$$
DELIMITER ;
example:
select json_extract_c(json, "$.totalDays"), json from item limit 100;

CREATE TABLE `json_test` (
 `id` int(11) DEFAULT NULL,
 `person_desc` text COLLATE utf8mb4_unicode_ci
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
insert INTO json_test values(2,'{"firstName":"Sergei","lastName":"Rachmaninoff","instrument":"piano"}');
SELECT id,json_extract_c(person_desc,'$.lastName') as "keys" FROM json_test;

CREATE DEFINER=`zhangfen`@`%` FUNCTION `json_extract_c`(
details TEXT,
required_field VARCHAR (255)
) RETURNS text CHARSET latin1
BEGIN
SET details = SUBSTRING_INDEX(details, "{", -1);
SET details = SUBSTRING_INDEX(details, "}", 1);
RETURN TRIM(
  BOTH '"' FROM SUBSTRING_INDEX(
    SUBSTRING_INDEX(
      SUBSTRING_INDEX(
        CONCAT('"":"",',details),
        CONCAT(
          '"',
          SUBSTRING_INDEX(required_field,'$.', -1),
          '":'
        ),
        -1
      ),
      ',"',
      1
    ),
    ':',
    -1
  )
) ;
END